High temperature flame spray powder



United States Patent Ofllice 3,313,633 Patented Apr. 11, 1967 3,313,633HIGH TEMPERATURE FLAME SPRAY PGWDER Frank Nicholas Longo, Mineola, N.Y.,assignor to Metco, Ina, Westbury, N.Y., a corporation of New Jersey NDrawing. Filed July 24, 1963, Ser. No. 297,198 11 Claims. (Cl. 106-1)This invention relates to a high temperature flame spray powder andprocess.

The invention more particularly relates to a flame spray powder mixturecontaining a self-fluxing alloy powder and a powder of a metal whichmelts at a high temperature, such as tungsten, rhenium, tantalum,molybdenum, columbium, or alloys thereof, and to a process for flamespraying such powder mixtures at high temperatures to produce dense,coherent coatings which show excellent wear and load-resistantcharacteristics.

In the flame spray art, there is a well known class of powders which arecommonly referred to as spray-weldable, self-fluxing metal powders, orsimply as self-fluxing alloy powders. Such powders are, for example,described in United States Patent Nos. 2,875,043 of Feb. 24, 1959, and2,936,229 of May 10, 1960. These powders contain a base metal, such asnickel or cobalt, and a constituent to provide fluxing properties, suchas boron or preferably boron and silicon. The powders are mostfrequently used for applying fused coatings to steel or steel-alloybases by a process known as spray welding. The spray welding processinvolves the steps of first spraying the powder onto the surface to becoated, using the conventional flame-spray process, and thereafterfusing the coating in place. The fusing may be done, for example, in afurnace, by means of induction heating or the like, but is often done bydirectly heating the coated surface with a heating torch.

The flame spraying is the sprayweld process is simply a mode ofpositioning the alloy powder on the surface to be coated in order toallow the fused coating to be formed by the subsequent fusing operation.The coating thus sprayed prior to the fusing operation is porous, is notfirmly bonded in place, and is not useful in the same manner assubsequent fused coatings, i.e. is not a hard, dense, wear-resistantsurface. The particles of a groundfinished, as-sprayed coating, will forexample pull out when pressure-sensitive tape, such as Scotch tape, isapplied and then stripped off.

It is an object of this invention to provide a flame spray powdermixture containing a self-fluxing alloy powder which may be sprayed,under special conditions of temperature, to produce dense, coherentcoatings which are similar in certain respects to fused coatings formedby the sprayweld process but which do not require a subsequent fusingoperation.

A further object of this invention is a process for producing dense,wearand load-resistant coatings, utilizing a flame spray powder mixturecontaining a self-fluxing alloy powder.

These and still further objects will become apparent from the followingdescription:

In accordance with the invention I have discovered that if conventionalself-fluxing alloy powder is flame-sprayed in admixture with about to95% and preferably 15 to 30% by weight, or alternately 70 to 90% byweight, of a metal powder having a melting point above 3500 F.,

and preferably from the group consisting of tungsten, rhenium, tantalum,molybdenum, columbium, and alloys thereof having a melting point above3500 F. under flame spray conditions which will cause a melting of thehigh melting point metal, as for example utilizing a plasma flame, thatsuperior, dense, strong, wearand load-resistant coatings are formed,which for instance show superior properties as bearing and other wearandload-resistant surfaces.

The meal powder which is admixed with the self-fluxing alloy powderpreferably should have a melting point above 4000 F., as for examplebetween 4600 and 6200 F. The percents by weight of the higher meltingpoint powder, as given herein, refer to the percents by weight based onthe mixture of this powder with the self-fluxing alloy powder.

The high melting powder component which makes up the 5 to by weight ofthe mixture thereof with the self-fluxing alloy powder need not be asingle metal powder but may be a mixture of one or more separate metalpowders and/ or alloys as specified, as for example a mix ture of any oftungsten, rhenium, tantalum, molybdenum, columbium and/or their alloys.

The self-fluxing alloy powder used in accordance with the invention maybe any known or conventional selffluxing alloy powder, as for exampleany of the powders described in United States Patent Nos. 2,875,043 and2,936,229. These powders are often referred to as selffluxing sprayweldor spray-weldable powders but the term self-fluxing alloy powders willbe generically used herein and in the claims to designate thesematerials. The self-fluxing alloy powders are preferably of the nickelor cobalt type containing boron, and most preferably boron and siliconas the self-fluxing element. The most preferable self-fiuxing alloypowders are of the nickel or nickelchromium alloy type containing boronand silicon. In addition to the base metal, i.e. the nickel and/ orcobalt and the fluxing element or elements, the powder may be formed ofadditional alloy components, as for example up to 20% chromium, toimpart corrosion and oxidation resistance, carbon in an amount of notmore than a few percent, iron in an amount not exceeding about 10%, andpreferably not exceeding about 5% in weight of the total alloy.

An example of a typical self-fluxing alloy powder of the boron-nickeltype consists of 0.7l% carbon, 3.5- 45% silicon, 2.75 to 3.75% boron,35% iron, up to 18% chromium, as for instance 16-18% chromium withnickel making up the balance.

An example of a typical sprayweld alloy of the cobalt base type may, forexample, contain 1 /2 to 3% boron, 04.5% silicon, 03% carbon, 0'20-%chromium, 030% nickel, 020% molybdenum, 020% tungsten, and the balancecobalt.

The self-fluxing alloy powder should generally have a particle sizebelow mesh US. Standard screen size. When intended for spraying with aplasma flame in accordance with the preferred embodiment of theinvention, the particles should be of a size between 100 mesh and +8microns and preferably between 230' mesh and +15 microns.

The high melting point metal powder used in admixture with theself-fluxing alloy powder must be a metal powder having a melting pointabove 3500 and preferably albove 99.42% molybdenum-5% titaniurn.08%zirconium 90% tantalum-10% tungsten 85% tantalum-10% hafnium-5% tungsten50% rhenium-50% molybdenum 80% columbiuml% molybdenum-10% titanium Anymixture of these metal powders or alloy powders may also be used. Themost preferable metal powders are powders of tungsten, tantalum, ormolybdenum, or alloys thereof having a melting point between 4600" F.and 6200" F.

The high melting point metal powder must be a metal per se and cannot bein the form of a refractory oxide, carbide, or the like. Furthermore,the high melting point metal powder must be independent of theself-fluxing alloy powder and may not be alloyed therewith or the like.The particle size of the high melting point metal powder should besimilar to that of the self-fluxing alloy powder and should generally bebetween 100 mesh and +8 microns, and preferably between 270 mesh and +8microns, the mesh sizes being US. Standard screen sizes.

The high melting point metal powder must be present in an amount ofabout to 95% by weight and preferably 15 to 30%, or alternatively 70 to90%, by weight based on the total weight of the mixture thereof with theselffluxing alloy powder.

The powder mixture in accordance with the invention is preferablysprayed per se but may be sprayed in admixture or in conjunction withother spray materials, as for example, aluminum; or refractory carbides,such as carbides of tungsten, tantalum, titanium, etc., with or withouta cobalt or nickel matrix; refractory oxides, such as aluminum oxide orzirconium oxide, molybdenum disilicide, etc. The powder mixture inaccordance with the invention may, for example, be sprayed in amounts of595%, or preferably 90%, by weight of the other spray material, saidpercentage being based on the total mixture.

The powder mixture is preferably sprayed in a powder type flame spraygun but must be sprayed under conditions of temperature which will causemelting of the high melting point metal powder component. For thispurpose the temperature in the heating zone should exceed 4000 F. andshould preferably exceed 7000 F.

tungsten-25 rhenium.

The spraying in accordance with the invention is preferably effectedwith a plasma flame spray gun, as for example of the type which producesa plasma flame by constricting an electric arc in a nozzle with aplasma-forming gas, for instance nitrogen or argon alone, or in mixturewith hydrogen. Guns which produce a plasma flame in this manner are, forexample, described in US. Patent 2,960,- 594.

It is also possible to effect the spraying in a wire-type gun, with thepowder mixture held in spray wire or rod shape by a binder, as forexample a synthetic plastic, for example in the manner described in US.Patent 2,- 570,649, of Oct. 9, 1951. The term powder as used herein isgenerically intended to designate not only powder in a loose form, butpowder in such bonded form. In such case the wire-type gun must utilizea flame of sufficient temperature to melt the high melting point metal,as for instance a plasma flame.

In all other respects the spraying is effected in the wellknown andconventional manner for flame spraying, particularly for flame sprayingwith a plasma flame spray gun.

The coatings may be formed on conventional surfaces, as for example ironand steel alloyed surfaces for any purposes which require a wearand/ orload-resistant surface. Coatings of a depth of between .002 and 0.125"

and preferably between .005 and 0.030" may be formed, and are extremelyuseful as bearing surfaces, as for example on crankshafts subject tohigh loading forces. The coatings in accordance with the invention mayalso be used for forming polished rod liners, pump plungers,medium-to-high temperature-resistant steel roller bearings, furnacerolls, engine valve trim, glass molds, engine piston tops and annealingrolls or the like.

The surface which is sprayed in accordance with the invention should beprepared in the well known and conventional manner for flame spraying,for example with steel grit propelled with air at a pressure of 100 lbs.per square inch, or surface rolled in any other conventional manner, asfor example rough-threading, coating, or the like. In addition to ironand steel, copper, brass, aluminum, titanium, molybdenum, or any othermaterial whose surface is suitable for flame spraying by conventionalmethods, may be coated with the powder and by the process in accordancewith the invention.

While the coatings produced in accordance with the invention may besubstituted in their as sprayed condition for the fused coatingsproduced by the sprayweld process, they are not identical to these fusedcoatings, and in certain respects are superior thereto. The structure isdifferent, in that individual high melting point metal particles canuseually be individually identified in metallographically preparedsections. While the coatings in accordance with the invention do notrequire a subsequent fusing operation and are generally utilized withoutfusing, the same may be fused or heat-treated in many cases, forming adesirable, high-melting alloyed coating.

The following examples are given by way of illustration and not oflimitation:

EXAMPLE 1 Percent B 3.5 Si 4 Fe 4 Cr 17 C 1.0 Nickel Balance The powdermixture is flame-sprayed on a mild steel plate which was degreased andthen blasted with Gl8 steel grit, propelled with air at a pressure of100 p.s.i.g.

The spraying is effected at a distance of 4-6 from the plate, using theplasma flame spray gun Type 2M, as sold by Metco, Inc., of Westbury,N.Y., operated at 500 amps, -85 volts, to produce a plasma temperatureof l0,000 F.

The spraying is effected at a rate of 6 to 7 lbs. of powder per hour,using nitrogen at a pressure of 50 p.s.i.g. and a flow rate of CFH, andhydrogen at a pressure of 50 p.s.i.g. and a flow rate of 15 CFH. Thespray coating produced on the base is a dense coating which is built upto a layer thickness of 0.030". The preliminary grind-finish of thesprayed coating was 7 micro inches as compared to the ordinary 30-40micro inch finish for conventional sprayed coatings.

When Scotch tape was applied to the ground-finish surface of the coatingand then stripped away, there was very little particle pull-out ascompared with considerable particle pull-out which may be observed withthe conventional as sprayed sprayweld coatings.

EXAMPLE 2 Example 1 is repeated on the bearing surfaces of a crank shaftfor an internal combustion engine having an outer diameter of 2" for themain bearings and 1 /2" for the connecting rod bearings. The bearingsurfaces, as formed, are excellent, wear-resistant bearing surfaces,which are able to withstand the extremely high loading forces of modernengines.

EXAMPLE 3 Example 1 is repeated using, however, a self-fluxing alloy ofthe following composition: Fe 2.5%, Cr C .l5%, Si 2.5%, B 2.5%, Nibalance, and tungsten powder of a size between 325 mesh and +8 microns,in a mixture ratio of 75% of the self-fluxing alloy powder and 25% ofthe tungsten powder.

The coating produced had the appearance of wrought metal whenground-finished, and a surface finished of 5 micro inches was obtained.

EXAMPLE 4 Example 1 is repeated using the following powder mixtures ofthe particle size, composition and proportions indicated:

(a) 80% by Weight of tungsten of a particle size between 200 mesh and+30 microns, 20% of the selffluxing alloy of Example 3 of a particlesize between +270 mesh and +8 microns (b) 80% by weight of molybdenum ofa particle size between 170 and +325 mesh and 20% of the selffluxingalloy of Example 1 (c) by weight of tungsten of a particle size between270 mesh and +8 microns, 15% of molybdenum of a particle size between+270 mesh and +8 microns, 70% of the self-fluxing alloy powder ofExample 1 (d) 25 by weight of a tungsten-rhenium alloy containing 25%rhenium of a particle size between +270 mesh and +8 microns, and 75 ofthe self-fluxing alloy of Example 1.

In each case an extremely high tensile-strength, dense coating isobtained, for example a coating obtained with (a) above has a tensilestrength which is double that obtained when conventionally sprayingtungsten per se. When this coating is post heat-treated at 1900 F. fortwo hours in an inert atmosphere, the resulting coating will alloy andhave a melting point above 4000 F EXAMPLE 5 Several mixtures of theself-fluxing alloy of Example 1 with molybdenum powder of a particlesize between l40 mesh and +15 microns and in the following proportionswere made up:

90% self-fluxing alloy, 10% molybdenum 70% self-fluxing alloy, 30%molybdenum 50% self-fluxing alloy, 50% molybdenum.

These mixtures were each sprayed with the oxygenacetylene powder flamespray gun sold by Metco, Inc, Westbury, N.Y., as the ThermoSpray gun.Spraying was effected on cold rolled steel which had been blasted withG-18 steel grit under a pressure of 100 p.-s.i.g. of air at a distanceof 68 inches, using acetylene at 12 p.-s.i.g. pressure and 30 flow rate,oxygen of 14 p.s.i.g. pressure and 30 flow rate, with 5 lbs. of powderper hour entrained in acetylene. In each case a coating which had thecharacteristics of a partially fused coating was obtained. The coatingsproduced in this manner are excellently suitable for repairing wornrolls and bearings.

In the examples, in place of the specific, self-fiuxing alloy powdersdescribed, any of the powders set forth in US. Patents 2,875,043 and2,936,229 or any other conventional self-fiuxing alloy powder may beused.

The percentages of the higher melting point powder as set fort-h in theclaims are indicated as based on the self-fiuxing alloy powder and thisspecifically design-ates that the percentages given are the percentagesof the sum of the high melting powder and the self-fluxing alloy powder.Thus, for example, 5% by weight of the higher melting powder based onthe self-fluxing alloy powder designates that of the combined weight ofthe higher melting powder and the self-fluxing powder 5% is attributableto the higher melting powder and to the selffluxing alloy powder.Similarly, 95% by weight of the higher melting powder based on theself-fiuxing alloy powder designates that of the sum of the weight ofthe higher melting powder and self-fluxing alloy powder 95 isattributable to the higher melting powder and 5% to the self-fiuxingalloy powder.

While the invention has been described in detail with reference tocertain specific embodiments, various changes and modifications whichfall within the spirit of the invention and scope of the appended claimswill become apparent to the skilled artisan. The invention is thereforeonly intended to be limited by the appended claims or their equivalentswherein I have endeavored to claim all inherent novelty.

I claim:

1. A flame spray powder comprising a mixture of a boron containingnickel or cobalt base self-fluxing alloy powder and about 595% byweight, based on the total thereof with said self-fluxing alloy powder,of a powder of at least one metal selected from the group consisting oftungsten, rhenium, tantalum, molybdenum, columbium, and alloys thereofhaving a melting point about 3500 P. which powder is characterized byforming in its as flamesprayed condition an adherent coating on asubstrate.

2. A flame spray powder according to claim 1 in which said powder ofsaid group member is present in amount of about l530%.

3. A flame spray powder according to claim 1 in which said powder ofsaid group member is present in amount of about 70-90%.

4. A flame spray powder according to claim 1 having a particle sizebetween l00 mesh and +8 microns.

5. A flame spray powder according to claim 1 having a particle sizebetween 230 mesh and 8 microns.

6. A flame spray powder comprising a mixture of a boron containingnickel or cobalt base self-fluxing alloy powder and about 595% byweight, based on the total thereof with said self-fluxing alloy powder,of a powder of at least one refractory metal having a melting pointabove 3500 P. which powder is characterized by forming in its asflame-sprayed condition an adherent coating on a substrate.

7. A mixture of a self-fluxing metal powder, essentially consisting ofat least one base metal selected from the group consisting of nickel andcobalt and containing boron 'as a self-fiuxing element with about 5- 95%by weight of a tungsten powder, the powder mixture having a particlesize between and +8 microns which powder is characterized by forming inits as flame-sprayed condition an adherent coating on a substrate.

8. A mixture of a self-fluxing met-a1 powder, essentially consisting ofat least one base metal selected from the group consisting of nickel andcobalt and containing boron as a self-fluxing element with about 5'95%by weight of a tantalum powder, the powder mixture having a particlesize between l00 mesh and +8 microns which powder is characterized byforming in its as flame-sprayed condition an adherent coating on asubstrate.

9. A mixture of a self-fiuxing metal powder, essentially consisting ofat least one base metal selected from the group consisting of nickel andcobalt and containing boron as a self-fluxing element with about 595% byweight of a molybdenum powder, the powder mixture having a particle sizebetween l0-0 and +8 microns which powder is characterized by forming inits as flamesprayed condition an adherent coating on a substrate.

10. A mixture of a self-fiuxing metal powder, essentially consisting ofat least one base metal selected from the group consisting of nickel andcobalt and containing boron as a self-fluxing element with about 595% byweight of a columbium powder, the powder mixture having a particle sizebetween 1()0 mesh and +8 microns which powder is characterized byforming in its as flamesprayed condition an adherent coating on asubstrate.

11. A mixture of a self-fiuxing metal powder, essentially consisting ofat least one base metal selected from the group consisting of nickel andcobalt and containing boron as a self-fluxing element with about 5-95%by weight of a rhenium powder, the powder mixture having a particle sizebetween l00 mesh and +8 microns which 8 powder is characterized byforming it its as flame-sprayed condition an adherent coating on asubstrate.

References Cited by the Examiner UNITED STATES PATENTS DAVID L. RECK,Primary Examiner. HYLAND BIZOT, Examiner. R. O. DEAN, AssistantExaminer.

1. A FLAME SPRAY POWDER COMPRISING A MIXTURE OF A BORON CONTAININGNICKEL OR COBALT BASE SELF-FLUXING ALLOY POWDER AND ABOUT 5-95% BYWEIGHT, BASED ON THE TOTAL THEREOF WITH SAID SELF-FLUXING ALLOY POWDER,OF A POWDER OF AT LEAST ONE METAL SELECTED FROM THE GROUP CONSISTING OFTUNGSTEN, RHENIUM, TANTALUM, MOLYBDENUM, COLUMBIUM, AND ALLOYS THEREOFHAVING A MELTING POINT ABOUT 3500*F. WHICH POWDER IS CHARACTERIZED BYFORMING IN ITS AS FLAMESPRAYED CONDITION AN ADHERENT COATING ON ASUBSTRATE.